1 Technical Field
The present invention relates to rotation angle estimation apparatuses for rotating electric machines.
2 Description of Related Art
There are known rotation angle estimation apparatuses for rotating electric machines. Theses apparatuses are configured to reduce noise generated due to application of high-frequency voltages for rotation angle estimation. More specifically, in these apparatuses, to reduce the noise, at least one of the following techniques are used: (1) increasing separation between the frequencies of the high-frequency voltages; (2) lowering the frequencies of the high-frequency voltages to fall outside the audible frequency range; and (3) lowering the amplitudes of the high-frequency voltages (see, for example, “An Adjusted Current Control System for Signal-injection-based Position Sensorless Control and Parameter Identification”, Suk-Hwa Jung et al., IEEJ Transactions on Industry Applications, Vol. 132, No. 3, pp. 418-425).
However, with the above techniques, it is impossible to sufficiently reduce the noise generated due to application of the high-frequency voltages. Moreover, the rotation angle estimation accuracy is sacrificed for reduction of the noise.